Hold-Up is when the power supply keeps supplying power to load before it drops below the specified voltage level. This voltage level and the corresponding hold-up time differ for different power supplies.

1. 3/3/23, 3:00 PM Hold-Up Capacitor: Value Calculations & Uses
https://oxeltech.de/en/hold-up-capacitor-calculations-and-use/#What_is_Hold-Up_Time 1/9
Home(https://oxeltech.de/en/)  Capacitors(https://oxeltech.de/en/category/capacitors/)

Hold-UpCapacitor: Calculationsand
Uses
(https://oxeltech.de/en/hold-up-capacitor-calculations-and-
use/)
Hold-Up Capacitor: Calculations And Uses
Share




What Is A Hold-Up Capacitor & When Do We
Need It?
In real-timecritical applicationssuch asavionicsandlife-supportsystems,itisveryimportantto
havean uninterruptablepower supplysupplyingadequatepower tothesystem.
Anysudden dropin power can jeopardizethesystem’sworking,leadingtofatalitiesin theworst-
casescenario.Hereisatypical switched-modepower supplyblockdiagram:
Acapacitor isplacedrightafter therectification blocktocater for thissudden drop(usuallyfrom
amain linepower outage).In caseof apower drop,thecapacitor can kickin andmaintain power
levelsfor theloaduntil thepower comesback.
What Is Hold-Up Time?
Hold-Upiswhen thepower supplykeepssupplyingpower toloadbeforeitdropsbelowthe
specifiedvoltagelevel.Thisvoltagelevel andthecorrespondinghold-uptimediffer for different
power supplies.
Generally,linear supplieshaveveryshorthold-uptimesandgotozeroalmostinstantaneously.
However,theswitched-modesuppliescan holdupuntil thepower comesbackon or theUPS gets
connected.
Thisisbecauseswitched-modepower supplieshavehold-upcapacitorsafter therectification
stagethatkeepthepower within given levels.
How To Calculate The Value Of Hold-Up Capacitor?
Ithasbeen establishedearlier thatswitched-modepower suppliesusehold-upcapacitorstohold
thepower level aboveaspecificlevel in caseof power cuts.
Nowtocalculatethevalueof such acapacitor,thesupply’shold-uptimeissetfirst.Secondly,the
outputvoltageandcurrentvaluesaretobeknown tocalculatepower.Thispower valueistobe
usedlater for capacitor valuecalculation.
Usingthepower relation,wecan calculatetheoutputpower thatthecircuitprovidestoload:
P[W] =V . I [V,A]
Wealsocalculatetheenergystoredin agiven capacitor:
• WhatisaHold-UpCapacitor&WhenDoWeNeedIt?
•What is Hold-Up Time?
•How to CalculatetheValueofHold-Up Capacitor?
•References Oxeltech

2. 3/3/23, 3:00 PM Hold-Up Capacitor: Value Calculations & Uses
https://oxeltech.de/en/hold-up-capacitor-calculations-and-use/#What_is_Hold-Up_Time 2/9
Share




E[J] =½ . C . (V –V )
HereV isthevoltageatthebeginningof dischargetime,i.e.thenominal outputvoltage,andV is
thevoltageattheendof capdischargetime,i.e.thesafelimitfor hold-uptime.
Weknowthatpower isenergyper unitof time,sowecan usethisrelation andwritetheenergy
relation in termsof power andtime.After that,theequation can berearrangedtofindthe
capacitancevalue:
C[F] =(2 . P[W] . t[s] )/ (V –V )
Let’sdoan exampleandusethisrelation tofindthehold-upcapacitor for asystem:
Example: Thehold-uptimeof aswitched-modepower supplyis10ms.Theoutputvoltageissetto
5V,andthecurrentis1A.Thesafevoltagelimitfor thehold-upis4.8V.Findthevalueof thehold-
upcapacitor.
Wecan firstfindthepower suppliedbythecapacitor:
P[W] =V . I [V,A]
P =5W
Therelation for energyisgiven here:
E[J] =½ . C . (V –V )
HereV isthevoltageatthebeginningof dischargetime,i.e.5V,andV isthevoltageattheendof
capdischargetime,i.e.4.8V.
Now,wecan rearrangethistofindthecapacitancevalue:
C[F] =(2 . P[W] . t[s] )/ (V –V )
HereP[W] =E[J]/t[s] relation isusedtoreplaceenergy.
Thefinal valuefor thecapacitor comesouttobe:
C[F] =0.0510204081633F
OR
C[μF] =51020.40 μF
Thereyou go!
2
U
2
L
U L
2
U
2
L
2
U
2
L
U L
2
U
2
L
Oxeltech

3. 3/3/23, 3:00 PM Hold-Up Capacitor: Value Calculations & Uses
https://oxeltech.de/en/hold-up-capacitor-calculations-and-use/#What_is_Hold-Up_Time 3/9
Share




Nowwecan understandtheusageof ahold-upcapacitor andincorporateitintoour design
decisionsfor switched-modepower supplies.Moreover,wecan calculatethevalueof such a
capacitor accordingtoour specificapplication.
References
1.https://en.cosel.co.jp/technical/qanda/a0066_1.html
(https://en.cosel.co.jp/technical/qanda/a0066_1.html)
If you are facing any difficulties with your Hold-Up Capacitor calculations or any general
hardware design challenge, feel free to Contact Us (https://oxeltech.de/en/contact-us/)for
our consultancy. You can check out our other Technical Blogs
(https://oxeltech.de/en/blog/)on various topics or visit our new website Oxeltech.de to
find all about our services (https://oxeltech.de/en/services/)and products.
Team Oxeltech
 November 6, 2022(https://oxeltech.de/en/2022/11/06/)
 7:17 am

No
Commen
ts
(https://oxeltech.de/en/hold-up-capacitor-
calculations-and-use/#respond)
Did You Enjoy This Article?
Join Oxeltech community and getupdated every weekWe have alotmore justforyou! Lets
join usnow
Email
Subscribe Now
 No charge  Unsubscribe anytime
Leave A Reply
Your email addresswill notbepublished.Requiredfieldsaremarked*
Comment*
Name*
Email *
Oxeltech

4. 3/3/23, 3:00 PM Hold-Up Capacitor: Value Calculations & Uses
https://oxeltech.de/en/hold-up-capacitor-calculations-and-use/#What_is_Hold-Up_Time 4/9
Share




Website
Savemyname,email,andwebsitein thisbrowser for thenexttimeI comment.
PostComment
Recent Post
How To Write A Driver For Accelerometer LIS3DSH In
Zephyr? (Https://Oxeltech.De/En/How-To-Write-A-
Driver-For-Accelerometer-Lis3dsh-In-Zephyr/)
January 16, 2023
SoC Vs SoM : System On Chip Vs System On Module
(Https://Oxeltech.De/En/System-On-Chip-Soc-Vs-
System-On-Module-Som/)
December 23, 2022
ESD Best Practices (Https://Oxeltech.De/En/Esd-Best-
Practices/)
December 6, 2022
How To Choose Between Microcontroller And FPGA For
Your Embedded Application?
(Https://Oxeltech.De/En/Fpga-Vs-Microcontroller/)
December 6, 2022
Hold-Up Capacitor: Calculations And Uses
(Https://Oxeltech.De/En/Hold-Up-Capacitor-
Calculations-And-Use/)
November 6, 2022
(https://oxeltech.de/en/how-
to-write-a-driver-for-
accelerometer-lis3dsh-
in-zephyr/)
(https://oxeltech.de/en/system-
on-chip-soc-vs-system-
on-module-som/)
(https://oxeltech.de/en/esd-
best-practices/)
(https://oxeltech.de/en/fpga-
vs-microcontroller/)
(https://oxeltech.de/en/hold-
up-capacitor-
Oxeltech

5. 3/3/23, 3:00 PM Hold-Up Capacitor: Value Calculations & Uses
https://oxeltech.de/en/hold-up-capacitor-calculations-and-use/#What_is_Hold-Up_Time 5/9
Share




MTBF: Concept And Application
(Https://Oxeltech.De/En/Mtbf-Concept-And-
Application/)
October 6, 2022
All About LiDAR Technology – Complete Guide
(Https://Oxeltech.De/En/Lidar-Technology/)
September 6, 2022
How To Choose The Right Flash Memory For Your
Embedded Application. (Https://Oxeltech.De/En/Flash-
Memory-In-Embedded-System/)
August 6, 2022
Altium’s PCB Designer Tools Guide
(Https://Oxeltech.De/En/Altium-Pcb-Designer-Tools-
Guide/)
July 6, 2022
Altiums Amazing Features – Project Management Tools
(Https://Oxeltech.De/En/Altium-Project-Management/)
June6, 2022
Ceramic Capacitors – Which Aspects To Consider When
Using Them In Your Design?
(Https://Oxeltech.De/En/Ceramic-Capacitor-Uses/)
May 8, 2022
(https://oxeltech.de/en/mtbf-
concept-and-
application/)
(https://oxeltech.de/en/lidar-
technology/)
(https://oxeltech.de/en/flash-
memory-in-embedded-
system/)
(https://oxeltech.de/en/altium-
pcb-designer-tools-
guide/)
(https://oxeltech.de/en/altium-
project-management/)
Oxeltech

6. 3/3/23, 3:00 PM Hold-Up Capacitor: Value Calculations & Uses
https://oxeltech.de/en/hold-up-capacitor-calculations-and-use/#What_is_Hold-Up_Time 6/9
Share




How To Control DC Servo Motors?
(Https://Oxeltech.De/En/Dc-Servo-Motor-Controller/)
April 21, 2022
Your Ultimate Guide To Designing Analog Filters
(Https://Oxeltech.De/En/Analog-Filters-Design-Guide/)
April 9, 2022
Consumer Electronics, Industrial Electronics And
Industrial Standards (Https://Oxeltech.De/En/Consumer-
And-Industrial-Electronics-Standards/)
April 1, 2022
Design Guide On USB-C PD Charge-Through Feature
With Data Role Swap (Https://Oxeltech.De/En/Usb-C-
Design-Guide/)
March23, 2022
Altium’s Team Collaboration Features In PCB Design
(Https://Oxeltech.De/En/Altium-365-Team-
Collaboration/)
March6, 2022
Using Zephyr OS For Interfacing An IMU Sensor With
NRF52 Over SPI (Https://Oxeltech.De/En/Using-Zephyr-
Os-For-Interfacing-An-Imu-Sensor-With-Nrf52-Over-
Spi/)
July 25, 2021
(https://oxeltech de/en/ceramic
(https://oxeltech.de/en/dc-
servo-motor-controller/)
(https://oxeltech.de/en/analog-
filters-design-guide/)
(https://oxeltech.de/en/consumer-
and-industrial-
electronics-standards/)
(https://oxeltech.de/en/usb-
c-design-guide/)
(https://oxeltech.de/en/altium-
365-team-
collaboration/)
(https://oxeltech.de/en/using-
zephyr-os-for-
Oxeltech

7. 3/3/23, 3:00 PM Hold-Up Capacitor: Value Calculations & Uses
https://oxeltech.de/en/hold-up-capacitor-calculations-and-use/#What_is_Hold-Up_Time 7/9
Share




Use Of Grounding Techniques In PCB Design To Prevent
Electromagnetic Interference (EMI)
(Https://Oxeltech.De/En/Pcb-Grounding-Techniques/)
June29, 2021
PCB Design Guidelines For Reduced Electromagnetic
Interference (EMI) (Https://Oxeltech.De/En/Pcb-Design-
Guidelines-For-Reduced-Electromagnetic-Interference-
Emi/)
May 5, 2021
EMC Vs EMI – Compatibility, Principles & Mechanism
Comparisons (Https://Oxeltech.De/En/Emc-And-Emi/)
April 18, 2021
interfacing-an-imu-
sensor-with-nrf52-over-
spi/)
(https://oxeltech.de/en/pcb-
grounding-techniques/)
(https://oxeltech.de/en/pcb-
design-guidelines-for-
reduced-
electromagnetic-
interference-emi/)
(https://oxeltech.de/en/emc-
and-emi/)
Continue Reading
Oxeltech

8. 3/3/23, 3:00 PM Hold-Up Capacitor: Value Calculations & Uses
https://oxeltech.de/en/hold-up-capacitor-calculations-and-use/#What_is_Hold-Up_Time 8/9
Share




How To Write A Driver For Accelerometer LIS3DSH In Zephyr?
(Https://Oxeltech.De/En/How-To-Write-A-Driver-For-Accelerometer-
Lis3dsh-In-Zephyr/)
Team Oxeltech• January 16, 2023
In our previousZephyr blog,welookedathowtointerfaceasimpleIMU–Accelerometer sensor
with Zephyr RTOS runningon NRF52832.Knowinghow
Read More (Https://Oxeltech.De/En/How-To-Write-A-Driver-For-Accelerometer-Lis3dsh-In-
Zephyr/)
SoC Vs SoM : System On Chip Vs System On Module
(Https://Oxeltech.De/En/System-On-Chip-Soc-Vs-System-On-
Module-Som/)
Team Oxeltech• December 23, 2022
WhatisSystem on Chip,SoC?ASystem on Chipor SoCisakeycomponentin EmbeddedSystems
today.An SoCreferstoa
Read More (Https://Oxeltech.De/En/System-On-Chip-Soc-Vs-System-On-Module-Som/)
(https://oxeltech.de/en/how-to-write-a-driver-for-accelerometer-lis3dsh-in-zephyr/)
(https://oxeltech.de/en/system-on-chip-soc-vs-system-on-module-som/)
Would You Like Some Info?
Name
Name
Email
Email
Message
Oxeltech

9. 3/3/23, 3:00 PM Hold-Up Capacitor: Value Calculations & Uses
https://oxeltech.de/en/hold-up-capacitor-calculations-and-use/#What_is_Hold-Up_Time 9/9
Share




Let's Discuss
Contact Us for any Queries
(mailto:info@oxeltech.de)
info@oxeltech.de
(mailto:info@oxeltech.de)

(tel:+4917664738476)
+49176 64738476 (Tel:+4917664738476)

(http
s://w
ww.li
nkedi
n.co
m/co
mpan
y/oxe
ltech
/)

HardwareDesign&Simulation(https://oxeltech.de/en/hardware-design-simulation/)
PCB Layout &Assembly(https://oxeltech.de/en/pcb-layout-assembly/)
FirmwareDevelopment(https://oxeltech.de/en/firmware-development/)
Imprint(https://oxeltech.de/en/imprint/)
Contact Us(https://oxeltech.de/en/contact-us/)
Blog(https://oxeltech.de/en/blog/)
Member Of IHK (Https://Www.Ihk.De/)
Message
Send
Oxeltech