Transient voltage suppressor
A transient voltage suppressor may include a silicon controlled rectifier (SCR) having an anode coupled to Vcc. The SCR may include a PNP transistor (Q 2 ) and an NPN transistor (Q 3 ), the PNP transistor having a base in common with a collector of the NPN transistor and the PNP transistor having a collector in common with a base of the NPN transistor. The TVS may further include a Zener diode having an anode and cathode, wherein the anode is directly coupled to the base of the NPN transistor and/or the cathode is directly coupled to the base of the PNP transistor, and an additional NPN transistor (Q 1 ). The cathode of the SCR may be directly coupled to a base of the additional NPN transistor, and a collector and emitter of the additional NPN transistor may be directly coupled in series between V CC and ground.
1. A transient voltage suppressor for protecting components coupled to a power supply configured to provide a supply voltage Vcc, the transient voltage suppressor comprising:
a silicon controlled rectifier (SCR) having an anode coupled to a first terminal configured to supply voltage at Vcc, the silicon controlled rectifier comprising a PNP transistor (Q 2 ) and an NPN transistor (Q 3 ), the PNP transistor Q 2 having a base in common with a collector of the NPN transistor Q 3 and the PNP transistor having a collector in common with a base of the NPN transistor Q 3 ;
a Zener diode having an anode and cathode, wherein the anode is directly coupled to the base of the NPN transistor Q 3 and the collector of the PNP transistor Q 2 , and the cathode is coupled with Vcc; and
an additional NPN transistor (Q 1 ), wherein the cathode of the SCR is coupled to a base of the additional NPN transistor Q 1 , and wherein a collector and emitter of the additional NPN transistor Q 1 are coupled in series between Vcc and ground; and
a second Zener diode arranged with its cathode coupled in common to the base of the PNP transistor Q 2 and the collector of the NPN transistor Q 3 .
2. The transient voltage suppressor of claim 1 , wherein transistors Q 1 -Q 3 are mutually configured such that:
V CE ,Q 1 , <V CE ,Q 2 +V BE ,Q 3 , or
V CE ,Q 1 <V BE ,Q 2 +V CE ,Q 3,
where V CE , Q 1 is the collector-emitter saturation voltage on transistor Q 1 ,
V CE ,Q 2 is the collector-emitter voltage on transistor Q 2 ,
V BE ,Q 3 is the base-emitter forward voltage on transistor Q 3 ,
V BE ,Q 2 is the base-emitter forward voltage on transistor Q 2 , and
V CE ,Q 3 is the collector-emitter voltage on transistor Q 3 .
3. The transient voltage suppressor of claim 1 , wherein the Zener diode is configured to trigger the SCR after receiving a high voltage pulse.
4. The transient voltage suppressor of claim 3 , wherein current from the triggered SCR is arranged to turn on Q 1 .
5. The transient voltage suppressor of claim 4 , wherein Q 1 is arranged to conduct current at a voltage level of about 1V.
6. The transient voltage suppressor of claim 4 , wherein collector-emitter voltage on Q 1 is sufficiently low after turn-on of Q 1 to trigger the SCR to turn off.
7. The transient voltage suppressor of claim 1 , wherein the cathode of the Zener diode forms a common connection to the collector of Q 1 and an emitter of Q 2 .
8. The transient voltage suppressor of claim 1 ,
wherein the anode of the second Zener diode is coupled with the emitter and base of Q 1 and the emitter of Q 3 .
9. A method of providing transient voltage suppression for protecting components coupled to a power supply configured to provide a supply voltage Vcc, comprising:
providing a silicon controlled rectifier (SCR) having an anode coupled to a first terminal configured to supply voltage at Vcc, the silicon controlled rectifier comprising a PNP transistor (Q 2 ) and an NPN transistor (Q 3 ), the PNP transistor Q 2 having a base in common with a collector of the NPN transistor Q 3 and the PNP transistor Q 2 having a collector in common with a base of the NPN transistor Q 3 ;
providing a Zener diode having an anode and cathode, wherein the anode is coupled to the base of the NPN transistor Q 3 and the collector of the PNP transistor Q 2 , and the cathode is coupled with Vcc;
providing a second Zener diode arranged with its cathode coupled in common to the base of the PNP transistor Q 2 and the collector of the NPN transistor Q 3 ; and
providing an additional NPN transistor (Q 1 ), wherein the cathode of the SCR is coupled to a base of the additional NPN transistor, and wherein a collector and emitter of the additional NPN transistor are coupled in series between Vcc and ground,
wherein when Q 1 is turned on, Q 1 to conduct current at a voltage level of about 1V.
10. The method claim 9 , further comprising: receiving a high voltage pulse; and
triggering the SCR using the Zener diode.
11. The method of claim 10 , further comprising feeding current from the triggered SCR to turn on Q 1 .
12. The method of claim 11 , comprising configuring collector-emitter voltage of Q 1 after turn-on of Q 1 to trigger the SCR to turn off.