Abstract A DMOST driver circuit responds to the current flowing in the DMOST (13) and the voltage appearing across it. The current and voltage are multiplied together in a gm amplifier (18) which is coupled to drive a first input of a diff-amp (14). The diff-amp (14) has its second input (25) coupled to a source of reference potential (Vref). The diff-amp (14) output is coupled to the DMOST gate to create a stabilizing negative feedback loop. The first diff-amp input is also coupled to a reference potential related threshold voltage so that the drive to the DMOST (13) will be controlled by the DMOST power dissipation multiplied by a predetermined constant which is chosen to provide a safe dissipation level.
A circuit for limiting the power dissipation in a DMOST (13) to a safe value comprising: means (23, 24) for sensing the voltage across said DMOST; means (17) for sensing the current passing through said DMOST; means (18) for multiplying the sensed voltage by the sensed current to obtain a power dissipation related current; and means (14) responsive to said dissipation related current to control the gate voltage of said DMOST to limit said power dissipation to a safe value.
Claim 2
Dependent Claim
80 words
A circuit for limiting the power dissipation in a DMOST (13) to a safe value comprising: means (23, 24) for sensing the voltage across said DMOST; means (17) for sensing the current passing through said DMOST; means (18) for multiplying the sensed voltage by the sensed current to obtain a power dissipation related current; and means (14) responsive to said dissipation related current to control the gate voltage of said DMOST to limit said power dissipation to a safe value.
Claim 3
Dependent Claim
34 words
The circuit of claim 1 wherein said means for sensing the current comprise a resistor (17) having a value that is small compared wih the DMOST on resistance coupled in series with said DMOST.
Claim 4
Dependent Claim
23 words
The circuit of claim 1 or 2 wherein said means for sensing voltage comprise a resistor (24) coupled in parallel with said DMOST.
Claim 5
Dependent Claim
14 words
The circuit of claim 2 or 3 wherein said resistor(17) is composed of metallization.
Claim 6
Dependent Claim
17 words
The circuit of one of claims 1-4, wherein said means for multiplying comprise a transconductance amplifier (18).
Claim 7
Dependent Claim
51 words
The circuit of claim 5 wherein said transconductance amplifier has a differential input that is connected to said means for sensing current and a common input that is connected to said means for sensing voltage whereby said transconductance amplifier output is a current that is proportional to voltage multiplied by current.
Claim 8
Dependent Claim
31 words
The circuit of claim 6 wherein said transconductance amplifier is composed of transistors (19-22) each of which includes plural emitters which are cross coupled to achieve a high degree of balance.
Claim 9
Dependent Claim
37 words
The circuit of one of the preceding claims wherein said means for multiplying is a transconductance amplifier that has an inverse temperature coefficient of transconductance that offsets a positive temperature coefficient of said voltage sensing means (17).
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