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![2 Types; Silicone Controlled Rectifier, [SCRSCR]
Unijunction Transistor, [UJTUJT]
Both are classified in the family of electronic switches called,
Thyristors.
Electronic Switches are; 1. Faster
2. Less Expensive
3. Last Longer
4. Have No Arc or Spark as do
manual switches & relays.
Applications SCR; 1. High Voltage & Current
>2000 V & >1500 A
2. Speed Controls for motors
Applications UJT; 1. Trigger for an SCR
2. Oscillator
Special Purpose DevicesSpecial Purpose Devices
SCR](https://image.slidesharecdn.com/06-scrujt-140616010648-phpapp01/85/06-scr-ujt-3-320.jpg)
![SCR, Gated ON
G
A
K
PP
PP
NN
NNGATE, G
ANODE, A
CATHODE, K
4 Layer PNPN Device, W/3 PN Junctions.
Looks like a diode, acts like a diode, current flows like a diode, W/ an
extra element called a Gate.
A small + DC or + spike applied to the Gate will turn on [Gated On] the
device provided forward biasing is set on the Anode & Cathode. Once
ON, Stays ON.
To Turn OFF, forward biasing must be removed or reversed Biased.
The GATE WILL NOT SHUT DOWNGATE WILL NOT SHUT DOWN conduction. [Latching Current must be
removed].
Special Purpose DevicesSpecial Purpose Devices
SCR; Silicone Controlled Rectifier.](https://image.slidesharecdn.com/06-scrujt-140616010648-phpapp01/85/06-scr-ujt-4-320.jpg)
![SCR;SCR; Silicon Controlled Rectifier.
Referred to as a Gated Diode.
To Turn ON, F Bias + on Gate Cathode junction.[ Gated On]
To Turn OFF, R Bias Anode/ Cathode thus removes
Latching current.
Latching Current, the minimum amount of current that can flow
through an SCR and hold it in the Break over condition or
conduction.
UJT;UJT; Unijunction Transistor.
Referred to as a Double Based Diode.
Location of the emitter joined to the N material [PN Junction]
determines the amount of voltage required @ the emitter to cause
conduction through the Emitter.
3 Waveforms Produced, + & - Spike, Saw tooth.
Main Use, Oscillator & Switching Trigger.
SCR & UJT;SCR & UJT; Both in the Family called Thyristors, [Electronic Switches].
Special Purpose Devices
SCR & UJT; Terms.
Review Questions](https://image.slidesharecdn.com/06-scrujt-140616010648-phpapp01/85/06-scr-ujt-16-320.jpg)
Uploaded byGowtham P
06 scr & ujt
The document discusses two specialized semiconductor devices - the unijunction transistor (UJT) and the silicon controlled rectifier (SCR). It provides details on their operation and applications. Specifically: - The UJT and SCR are specialized transistors that act as electronic switches. They are smaller, more efficient, and reliable than previous switching devices. - The UJT can be used as a trigger for an SCR or in oscillator circuits due to its ability to produce spikes and a sawtooth waveform. The SCR is used in high-voltage, high-current applications like motor speed controls. - The document provides circuit diagrams and explanations of how each device works, including how they are turned on and off and
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06 scr & ujt
- 2. Since the developmentof the transistor, continuous research in the field of semiconductors has provided many additional semiconductor devices. Some if these devices have been adopted to applications that were normally impossible. These devices, now considered as innovations in military and commercial equipment, may become as commonplace as the junction transistor is today. Indications are that development and applications for solid state devices will continue to expand. In all cases, where other devices were previously used, the solid state devices are smaller, more efficient, less expensive, and more reliable. Two of these devices, the uni-junction transistor (UJT) and the silicon controlled rectifier (SCR), will be discussed in detail during this lesson. Special Purpose DevicesSpecial Purpose Devices
- 3. 2 Types; SiliconeControlled Rectifier, [SCRSCR] Unijunction Transistor, [UJTUJT] Both are classified in the family of electronic switches called, Thyristors. Electronic Switches are; 1. Faster 2. Less Expensive 3. Last Longer 4. Have No Arc or Spark as do manual switches & relays. Applications SCR; 1. High Voltage & Current >2000 V & >1500 A 2. Speed Controls for motors Applications UJT; 1. Trigger for an SCR 2. Oscillator Special Purpose DevicesSpecial Purpose Devices SCR
- 4. SCR, Gated ON G A K PP PP NN NNGATE,G ANODE, A CATHODE, K 4 Layer PNPN Device, W/3 PN Junctions. Looks like a diode, acts like a diode, current flows like a diode, W/ an extra element called a Gate. A small + DC or + spike applied to the Gate will turn on [Gated On] the device provided forward biasing is set on the Anode & Cathode. Once ON, Stays ON. To Turn OFF, forward biasing must be removed or reversed Biased. The GATE WILL NOT SHUT DOWNGATE WILL NOT SHUT DOWN conduction. [Latching Current must be removed]. Special Purpose DevicesSpecial Purpose Devices SCR; Silicone Controlled Rectifier.
- 5.
- 6. PC; 52A Special PurposeDevices SCR; Efficient Power use. P = I X E PLAMP = ILAMP X ELAMP PLAMP = 50 ma X 11v PPLAMPLAMP = 550 mW= 550 mW P = I X E PSCR = ISCR X ESCR PSCR = 50ma X 1v PPSCRSCR = 50 mW= 50 mW LAMP SCR 12VDC
- 7. Special Purpose Devices SCR;Control Ckt PC 52A. Operate Mode. OO NN EE R2 10 KΩ R1 1KΩ R3 100KΩ RESET OPERATEOPERATE S2 C1 1µf 1 2 3 4 5 +DC+DC S1 - 9- 9 VDCVDC +12+12 VDCVDC SCR ++ ++ L1 II Reset
- 8. PC 52B Special PurposeDevices SCR; Control Ckt PC 52A. Reset Mode. OO NN EE R2 10 KΩ R1 1KΩ R3 100KΩ OPERATE RESETRESET S2 C1 1µf 1 2 3 4 5 +DC+DC S1 - 9- 9 VDCVDC +12+12 VDCVDC SCR1 ++ -- L1 II Closing S2 Grounds the + plate on Cap C1 causing it to discharge thus Reverse Biases SCR1, ceasing Conduction.
- 9. Special Purpose Devices SCR;Ckt PC 52B. Conducting. G SCR1 2N1596 R2 100 Ω R3 100 KΩ R1 10 KΩ C1 4.7mfd 1mfd C2 1 2 4 5 6 7 3 L1 PC 52B, Cutoff
- 10. Special Purpose Devices SCR;Ckt PC 52B. Cutoff. G SCR1 2N1596 R2 100 Ω R3 100 KΩ R1 10 KΩ C1 4.7mfd 1mfd C2 1 2 4 5 6 7 3 L1 UJT
- 11. Continue UJT PP NN NN EE BB22 BB11 EE BASE 1BASE1 BASE 2BASE 2 RRB2B2 RRB1B1 Base 2Base 2 Base 1Base 1 EmitterEmitter NITA LESSON;NITA LESSON; Per Instructor Discretion. Special Purpose Devices UJT; Unijunction Transistor
- 12. Continue, UJT Ops SpecialPurpose Devices UJT; Unijunction Transistor The position of the emitter fusing on the N material determines how much voltage is required to turn on the UJT @ the Emitter. EE BASE 2 BASE 1BASE 1 RB2 RB1RB1 EE RB2 RRB1B1 BASE 2 BASE 1BASE 1 PP NN NN EE BB22 BB11 EmitterEmitter toto Base 1Base 1. RR↑↑, VV↑↑ EmitterEmitter toto Base 1Base 1. RR↓↓, VV ↓↓ Current, UJT isCurrent, UJT is ConductingConducting
- 13. Special Purpose Devices UJT;Oscillator PC 51. Operation, C1 Charge. 0 V 0 V 0 V C1 Charges C1 Discharges 1 3 5 Q1 2N4891 2 4 R3 470 Ω R4 100 Ω R1 18 KΩ R2 100 KΩ C1 .0015 µF 1212 VDCVDC The RC TC determines Charge Time & Frequency ++ C1 Discharge
- 14. Trouble Shoot Special PurposeDevices UJT; Oscillator PC 51. Operation, C1 Discharge. Output; ++ & -- Spike. Saw tooth @ TP3. 1 3 5 Q1 2N4891 2 4 R3 470 Ω R4 100 Ω R1 18 KΩ R2 100 KΩ C1 .0015 µF 1212 VDCVDC The RC TC determines Charge Time & Frequency ++ 0 V 0 V 0 V C1 Charges C1 Discharges + SPIKE+ SPIKE Output @Output @ TP2TP2 - SPIKE- SPIKE Output @Output @ TP4TP4
- 15. Special Purpose Devices UJT;Oscillator PC 51, 2 Ckt. What is the Malfunction?What is the Malfunction? NO Output R1 R2 C1 R3 R4 5 3 1 .0015µf 25µfC2 100KΩ R5 R6 R7 R8 2N4891 Q1 Q2 2N4891 100Ω 470Ω470Ω 47KΩ 1MΩ 2 4 8 7 9 10 O 5.01 VDC5.01 VDC 10.7 VDC10.7 VDC .214 VDC.214 VDC 10.7 VDC 0 VDC .214 VDC NO Output Terms
- 16. SCR;SCR; Silicon ControlledRectifier. Referred to as a Gated Diode. To Turn ON, F Bias + on Gate Cathode junction.[ Gated On] To Turn OFF, R Bias Anode/ Cathode thus removes Latching current. Latching Current, the minimum amount of current that can flow through an SCR and hold it in the Break over condition or conduction. UJT;UJT; Unijunction Transistor. Referred to as a Double Based Diode. Location of the emitter joined to the N material [PN Junction] determines the amount of voltage required @ the emitter to cause conduction through the Emitter. 3 Waveforms Produced, + & - Spike, Saw tooth. Main Use, Oscillator & Switching Trigger. SCR & UJT;SCR & UJT; Both in the Family called Thyristors, [Electronic Switches]. Special Purpose Devices SCR & UJT; Terms. Review Questions
- 17. 1. One ofthe main uses of a UJT is as a _________, __________ . 2. Why is the UJT often used instead of a conventional transistor? __________________________________________________ . 3. The UJT is also called a _________ _____ ______ . 4. What is the Basic purpose of a SCR? __________ ________ . 5. How is an SCR turned on ? __________________________ . 6. What family of transistors does the SCR & UJT belong to ? __________ . 7. Draw the schematic symbol for a UJT & SCR. 8. How many PN Junctions does the SCR contain ? ____ . 9. How is an SCR turned Off ? __________ _______ __________. Special Purpose Devices Review Questions; Answers; 1- 9
- 18. Answer; 10 Special PurposeDevices Review Questions; 10. Refer to PC 51; The following DC voltages are present: TP4 = 10.7 VDC, TP3 = 0 VDC, TP2 = .21 VDC. What is the Malfunction ? a. C1 Open b. R1 Open c. R2 Short d. Q1 Open 11 33 55 Q1Q1 2N48912N4891 22 44 R3R3 470470 ΩΩ R4R4 100100 ΩΩ R1R1 18 K18 KΩΩ R2R2 100100 KKΩΩ C1C1 .0015.0015 µµFF 1212 VDCVDC PC 51PC 51