COSINE Tier-1 distributor Jarwey｜COS3842BD PWM controller vs COS29752WU LDO on auxiliary rails
Jarwey is a COSINE Tier-1 distributor and can support selection, datasheets, samples, small lots, and lead time.
On an industrial housekeeping rail or an adapter, the first split is thermal, not the logo on the regulator. If (Vin−Vout)×Iout will not fit the copper and the case, start with an external-FET peak-current PWM controller, COS3842BD. If the bus is already close to the output and you only need an adjustable high-current post-regulator, shortlist the high-voltage LDOs COS29302 (3 A) or COS29752WU (7.5 A).
The 1.5–7.5 A current ladder and the UC3842-versus-SG3525 mode table already exist. This note does not repeat them. Datasheets: contact Jarwey.
Switching stage or linear post-regulator
| Job | Part | Open this page when | Bounds stated on the product page | Package | Search anchor (verify) | Page |
|---|---|---|---|---|---|---|
| External-FET switching controller | COS3842BD | Adapter, charger, or a large step-down; buck, boost, flyback, or forward | Peak current mode; controller Vin max 28 V | SOP-8 | UC3842 class | 984 |
| Linear post-reg, ~3 A | COS29302 | Intermediate bus already near the load; adjustable output and thermal shutdown matter | Vin 5–40 V; 3 A; 1.24 V adjustable feedback | TO-263-5 | MIC29302 class | 981 |
| Linear post-reg, ~7.5 A | COS29752WU | Same job, load current in the 7.5 A class | Vin 5–40 V; 7.5 A; 1.24 V adjustable feedback | TO-263-5 | MIC29752 class | 863 |
Do the arithmetic before opening a datasheet. Dropping 24 V to 5 V at 3 A is about 57 W in a linear pass element. That is a heatsink problem, not a reason to pick a higher-current LDO. Use COS3842BD for the switching stage. The controller supply pin is specified at 28 V max on the product page. A higher power bus needs an auxiliary feed into the IC; do not tie that bus straight to the controller Vin. Startup threshold and maximum duty cycle come from the datasheet Jarwey supplies.
A 1–2 V drop at 3 A or 7.5 A is where the catalog thermal shutdown and the 1.24 V feedback divider earn their place. The 1.5 A part is COS29152WU; the 5 A part is COS29502WU. Current-tier order is in the high-current LDO family note. Voltage-mode COS3525ADW (inverter / welder class supplies) is a different decision — see the PWM controller family note.
Checklist before you shortlist
- Heat: compute (Vin−Vout)×Iout first. A multi-amp, wide drop does not belong on a 7.5 A LDO.
- Controller bias: COS3842BD Vin max is 28 V. If the power stage is higher, feed VCC from an aux winding or a pre-regulator and check UVLO.
- Quiet load after the switcher: an ADC or a sensor may still want a small linear post-reg. The 7.5 A power LDO is not a sensor-noise part; do not screen it on PSRR numbers from a low-noise LDO brief.
- Current class: about 3 A → COS29302; about 7.5 A → COS29752WU. Write peak and continuous current as separate lines.
- External MOSFET: COS3842BD does not include the switch. Verify gate drive, the current-sense resistor, and slope compensation on the board.
- Anchors are not a drop-in: UC3842, MIC29302, and MIC29752 are search anchors only. Pinout, startup voltage, and current limit need the Jarwey datasheet and a sample build.
- Samples and lead time: ask Jarwey for the datasheet, a small lot, and delivery.
Datasheet and contact
Jarwey · COSINE Tier-1 distributor · kerry.w@jarwey.cn · Contact.
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