LT3750 Capacitor Charger Controller: Datasheet, Circuit, Equivalent

LT3750 Pinout

Pin Description

LT3750 Symbol

LT3750 Footprint

LT3750 3D Model

The LT3750 is a flyback converter designed to rapidly charge large capacitors to a user-adjustable target voltage. A patented boundary mode control scheme* minimizes transition losses and reduces transformer size. LT3750 can operate from a variety of power sources. A typical application can charge a 100µF capacitor to 300V in less than 300ms.

Linear Technology/Analog Devices LT3750EMS#PBF technical specifications, attributes, parameters and parts with similar specifications to Linear Technology/Analog Devices LT3750EMS#PBF.

■ Charges Any Size Capacitor

■ Easily Adjustable Output Voltage

■ Drives High Current NMOS FETs

■ Primary-Side Sense—No Output Voltage Divider Necessary

■ Wide Input Range: 3V to 24V

■ Drives Gate to VCC – 2V

■ Available in 10-Lead MS Package

■ Emergency Warning Beacons

■ Professional Photoflash Systems

■ Security/Inventory Control Systems

■ High Voltage Power Supply

■ Electric Fences

■ Detonators

LT3750 Block Diagram

LT3750 Typical Application Circuit-1

LT3750 Typical Application Circuit-2

LT3750 Typical Application Circuit-3

Equivalent for LT3750: LT3751

Anyone who has attempted to construct a high voltage capacitor charger understands how tough it is, especially when designing a circuit from the ground up. The end results are frequently inefficient and take a long time to charge. The LT3750 incorporates all of the operations of a capacitor charging circuit – voltage detection, MOSFET driving, and control logic – onto a tiny 10-pin chip.

Because it is a capacitor charger, the LT3750 is a basic implementation of a flyback converter without regulation (in the traditional sense).

Flyback converters take discrete packets of energy from one source, store them in a linked inductor ('transformer,' and transmit the energy to the secondary at a different voltage.

The LT3750 is a current mode device, which means that the peak primary current remains constant during the switching cycle. A resistor can be used to control the peak current. The resistor's value can be estimated using the following formula:

R_SENSE = 78mV / I_PEAK

The MOSFET is shut off when the current limit is reached, and the energy stored in the primary is transferred to the secondary. The secondary voltage (divided by the turns ratio) is reflected on the primary during this time, resulting in a voltage rise at the drain node compared to the supply. The RBG and RVOUT resistors on the LT3750 detect this difference, which is proportional to the output voltage. The formula for calculating the output voltage is:

VOUT = 1.24V * (RVOUT/RBG) * N

The turns ratio is denoted by N. The datasheet advises setting the RBG resistor value to 2.49K, preferably with a 1% tolerance.

The reflected voltage on the primary diminishes once the secondary energy transfer is complete. This is detected by the RDCM resistor, which initiates a new switching cycle. Again, 43K at 5% is the recommended value for the RDCM resistor. A 9A 300V charger is shown in the circuit below.

How to use LT3750

LT3750 Package

As a member of the S&P 500, Linear Technology Corporation is committed to designing, manufacturing and marketing an extensive line of high-performance analogue integrated circuits for main companies around the world. Between the analogue world and digital electronic products in communications, networks, industry, automobiles, computers, medical, instrumentation, consumer, military and aerospace systems, our products have built an important bridge for them. Our products include not only the production of power management, data conversion, signal conditioning, RF and interface ICs, μModule subsystems, but also wireless sensor network products.

Download datasheets and manufacturer documentation for Linear Technology/Analog Devices LT3750EMS#PBF.