Three Terminal Regulators & Overvoltage Protection. Bill Leonard N0CU

Transcription

1 Three Terminal Regulators & Overvoltage Protection Bill Leonard N0CU

2 Three Terminal Regulators 101 V IN IN 3 Term Reg ADJ OUT R1 V OUT (1.2-33V) Volt Adjust R2 Current & power dissipation limits vary with P/N & case style Available for both positive and negative supplies Maximum current is internally limited Case temperature is internally limited V OUT = V REF x (1+R2/R1) ~ 1.25 x (1+R2/R1) R2 ~ R1 x (V OUT -1.25)/1.25 Recommended R1 = 240 W R2 ~ 192 x (V OUT -1.25) MANY uses besides voltage regulation (see data sheet)

3 Three Terminal Regulators - Gotchas D1 V IN 0.1uF C1 IN 3 Term Reg ADJ OUT R1 V OUT C2 > 10uF Volt Adjust R2 R3 C1 is needed to insure stability (ie, no oscillations) C2 improves transient response D1 is needed to protect regulator V IN V OUT > 2.5 V (Spec) Case is usually connected to V OUT R3 may/may not be required I OUT must always be > 10 ma (Spec) for regulation to occur

4 Why Add Overvoltage Protection (OVP)? Whenever the cost of the load exceeds the cost of OVP Transients on AC power line Warranty concerns with new transceivers Commercial Power Supplies May Not Have Adequate Protection From eham reviews: MFJ-4245MV Switching Power Supply: MFJ-4245 is falsely advertising that this power supply has an overvoltage protection per specs...output went to about 35 volts! My IC-735 is now fried....my NEW FT950 transceiver was damaged....it burned up my 2m Rig... If you touch the output leads together, your 13 volt supply suddenly puts out 33 volts.

5 Typical Overvoltage Protection Approach Power Supply R1 xx Amps Fuse Voltage Regulator Regulated +V OUT +V SCR SCR Trigger Circuit Sense

6 Response Time of Fuses Fuses open based upon energy dissipated in the fuse Ampere squared seconds (I 2 t): The melting, arcing, or clearing integral of a fuse, termed I 2 t, is the thermal energy required to melt, arc, or clear a specific current. It can be expressed as melting I 2 t, arcing I 2 t or the sum of them, clearing I 2 t. UL listed or recognized fast acting fuses would typically open within 5 seconds maximum when subjected to 200% to 250% of its rated current.

7 Overvoltage Protection Circuit in ARRL Handbook Sense +V SCR

8 Overvoltage Protection Circuit in ARRL Handbook Problem 1: Transient Feedthru in Voltage Regulators

9 Transient Feedthru in Voltage Regulators

10 To Reduce Transient Feedthru in Voltage Regulators Make (R1 xc1) > 100 usec R1 + - C1

11 Overvoltage Protection Circuit in ARRL Handbook RT OUT Power Supply R1 xx Amps Fuse Voltage Regulator Regulated +V OUT RT TRIG +V SCR SCR Trigger Circuit Sense Problem 2: Two critical response times need to be addressed or the protection circuit may not protect the load Response Time at +V OUT (RT OUT ) Response Time of the Trigger Circuit (RT TRIG )

12 Response Time At Output (RT OUT ) Power Supply R1 xx Amps Fuse Voltage Regulator + - C1 Regulated +V OUT +V SCR SCR Trigger Circuit Sense RT OUT RT1 ~ R1 x C1 No C1 specified => RT1 = R1 x C1 = R1 x 0 = 0

13 Response Time of the Trigger Circuit (RT TRIG ) RT TRIG = RT SCR + RT2 ~ RT SCR + R2 x C2 ~ 1 usec + R2 x C2 RT TRIG RT2 R2 RT SCR ~ 1 usec C2

14 Response Time of the Trigger Circuit (RT TRIG ) RT2 ~ R2 x C2 =1000 ohms x Farad = sec = 1 msec R2 C2

15 Response Time of the Trigger Circuit (RT TRIG ) RT2 ~ R2 x C2 = 1 usec R2 C uf

16 Design Goal for Response Times RT2 ~ 1 usec RT1 ~ R1 x C1 RT1 > 10 x RT TRIG R1 R2 C2 + - C uf

17 Overvoltage Protection Circuit in ARRL Handbook Power Supply R1 xx Amps Fuse Voltage Regulator I L Regulated +V OUT +V SCR SCR Trigger Circuit Sense Problem 3: No specified minimum load current (I L )

18 Overvoltage Protection Circuit in ARRL Handbook Power Supply R1 xx Amps Fuse Voltage Regulator I L Regulated +V OUT RL +V SCR SCR Trigger Circuit Sense Problem 3: Most three terminal regulators must source 3-5 ma for regulation to occur

19 Overvoltage Protection Circuit in ARRL Handbook Power Supply R1 xx Amps Fuse Voltage Regulator + - C1 Regulated +V OUT +V SCR SCR Trigger Circuit Sense Problem 4: Most three terminal regulators should be protected from damage that could result from a short on the input

20 Overvoltage Protection Circuit in ARRL Handbook D1 Power Supply R1 xx Amps Fuse Voltage Regulator + - C1 Regulated +V OUT +V SCR SCR Trigger Circuit Sense Problem 4: Most three terminal regulators should be protected from damage that could result from a short on the input

21 Overvoltage Protection Circuit in ARRL Handbook R Protect D1 Power Supply R1 xx Amps Fuse Voltage Regulator + - C1 Regulated +V OUT +V SCR SCR Trigger Circuit Sense Problem 4: Maximum current through D1 should be limited whenever an overvoltage protection circuit is used

22 Overvoltage Protection Circuit in ARRL Handbook R Protect D1 Power Supply R1 xx Amps Fuse Voltage Regulator + - C1 Regulated +V OUT +V SCR SCR Trigger Circuit Sense Note: R1 & R Protect may need to be high wattage Don t want them to blow open when SCR fires

23 Solid Copper Wire Wire Size Fusing Current Resistance Gauge Amps Ohms/10 ft

24 Modified Overvoltage Protection Circuit R Protect D1 xx Amps R1 Power Fuse Voltage Supply Regulator + - C1 Regulated +V OUT V at Trigger = V Z V RT SCR ~ 1 usec RT2 = (1000) x 1x10-9 = 1 usec RT1 = R1 x C1 > 10 usec V at Trigger = +1.4 V 1 K Sense +V SCR V Z Volt Zener ½ W 1 K R2 C uf N2222 TYN640RG RL Max Voltage : 2N2222 = 30V 2N3501 = 150V Current Rating = 40 A Surge Current = 480 A Max Voltage = 600 V IG = 35 ma V at Trigger = +1.3 V V at Trigger = +0.7 V I G ~ 35 ma

25 ICOM V80 Power Supply With Overvoltage Protection 1W 5W 1N VDC 1W 5W 2 A Fuse 0.1uF RED +6.3 V LM350K YEL ORN 220W uf 35 V 680W A Max 1100W LED V at Trigger = +8.4 V 1 KW 7.5 Volt Zener ½ W V at Trigger = +1.3 V 1N W V at Trigger = V V at Trigger = +1.4 V 1 KW 2N2222 TYN640RG 1 KW uf 47W V at Trigger = +0.7 V I G ~ 35 ma Current Rating = 40 A Surge Current = 480 A Max Voltage = 600 V = 35 ma I G

26 ICOM V80 Power Supply With Overvoltage Protection 1W 5W 1N VDC 1W 5W 2 A Fuse 0.1uF RED +6.3 V LM350K YEL ORN 220W 1100W V at Trigger should be +8.9 V LED uf 35 V 680W A Max V at Trigger = +8.4 V 1 KW 7.5 Volt Zener ½ W V at Trigger = +1.3 V 1N W V at Trigger = V V at Trigger = +1.4 V 1 KW 2N2222 TYN640RG 1 KW uf 47W V at Trigger = +0.7 V I G ~ 35 ma Current Rating = 40 A Surge Current = 480 A Max Voltage = 600 V = 35 ma I G

27 Zener Diode Characteristics V Z 7.5 V Spec 0.5 V Voltage (V) V TRIG 7.0 V Current (ma)

28 Check your SCR after installation!!!!